Honestly, I enjoye the sc2 multiplayer for the most part. Ultimately I had to quit because I took losses far too seriously.. which is something i actually liked initially. Turns out, when you are particularly hard on yourself, and its possible to COMPLETELY blame yourself for a loss because of obvious retrospective mistakes, it wears on you pretty quickly.
That actually says a lot about you. That's one of the main reasons I play these kinds of games, because it helps me deal with my own insecurities.
For example, yesterday I went on about an 8-game losing streak. Now all these games turned out similar enough. I would do well, my team would usually do decently well (mostly because I was playing Eve mid and would gank constantly), and then lategame we would just throw it. This happened OVER and OVER and OVER again.
In my final game of the night, I was 15-3, and we had just won a major team fight. To celebrate this victory, our low health team (aside from MF, our ADC, who was full health) decided to go Baron because we had plenty of time. Unfortunately we didn't have time to push because a couple were still alive and the rest would have been up too quickly, but we had plenty of time to Baron.
So we ping Baron eight thousand times, and the whole team heads over there. What does MF do? She pushes the lane, gets up the enemy tower, and promptly dies to the remaining members of the enemy team. They take Baron and ultimately win the game.
So in essence, that MF just completely threw the game. There was no rhyme or reason for this, it was just sheer stupidity and refusal to cooperate with your team. A couple years ago I would have been so angry I would have been throwing things around my room (especially after a whole day of games like this). As it was, I just called him and idiot, told him it was his fault we lost, and reported him.
There was a little rage, but it was contained, and it's much better than my rage say, a few months ago. These games push my buttons, but it helps me deal with the consequences in a mature way, and ultimately makes me a better person I think.